Activity, Climate, and Postcranial Robusticity

Abstract

Postcranial robusticity--the massiveness of the skeleton--figures prominently in the debate over the origin of modern humans. Anthropologists use postcranial robusticity to infer the activity levels of prehistoric populations, and changes in robusticity are often used to support scenarios of adaptive change. These scenarios explain differences in morphology as the result of a change in lifestyle (habitual activity). One common scenario posits that early modern humans were more gracile than Neandertals because the modern humans' complex culture required less physical exertion. However, lifestyle is only one of many influences on morphology. Climate has clear correlations with physique and skeletal proportions. Analysis of recent humans that differ in terms of lifestyle and climatic adaptations reveals that limb bone robusticity varies with climate as much as or more than with lifestyle. Many of the differences in robusticity between Neandertals and early modern humans appear to be related to climatic adaptations. The results support the single-recent origin model of modern human origins. The differences in robusticity between Neandertals and early modern humans suggest that population replacement rather than local evolution best explains the emergence of modern humans in Europe. Both climatic adaptations (primarily body proportions) and lifestyle should be considered in analyses of robusticity.

Evolution of mechanoregulation of bone growth will lead to non-optimal bone phenotypes

“…In the age vs. weight data of McCammon (1970), a standard deviation of roughly 10% is present for many of the early years, which shows that ±10% is a good approximation for loading variability, as the loading is assumed to scale to weight vs. age data (van der Meulen et al, 1993). This variation represents the influence that environmental variation can have on the growth of a bone, such as the studies effects of nutrition (Kriegl et al, 2004), climate (Kobliansky et al, 2000;Pearson, 2000), exercise levels (Bass et al, 2002;Duncan et al, 2002), and a host of other environmental influences.…”

Ebb and flow or regional extinctions? On the character of Neandertal occupation of northern environments

“…Their bodies displayed pronounced musculature and varying levels of postcranial robusticity, especially high in the upper part of the body and in relation to manipulation activities [45]. This postcranial robusticity is related to a high level of activity generating intense biomechanical stress [8], but likely also partly related to Neandertals' adaptation to colder environments [31]. The Neandertals' large body mass and ecogeographical niche resulted in a costly body requiring a high basal metabolic rate (BMR).…”

The meaning of Neandertal skeletal morphology

“…Specifically, Neandertals have a wide pelvis, short limbs relative to trunk height, and short distal limb segments, whereas early modern humans have narrower bodies with relatively longer limbs (45,57,58,(65)(66)(67)(68)(69). These contrasts in body proportions have lead multiple researchers to propose that other postcranial differences between Neandertals and modern humans are simply secondary consequences of differences in body proportions.…”